Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum CHRISTIAN HJORT, JAN MANGERUD. LENA ADRIELSSON, STEIN BONDEVIK, JON Y. LANDVIK and OTTO SALVIGSEN Hjort, C., Mangerud, J . , Adrielsson, L . , Bondevik, S . , Landvik, J . Y . & Salvigsen 0. 199.5: Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum. Polar Research 14(2), 239-243. The common mussel Myrihu edulis is an indicator of milder marine conditions in the Arctic. with stronger Atlantic Water influx. during the Holocene and earlier interglacials. Twelve Holocene radiocarbon dates of Myrilus from eastern Svalbard fall between ca 8800 and SO00 BP and roughly delimit the marine climatic optimum period there. The beginning of this period in the east coincides with the immigration of boreal extralimital molluscs to western Svalbard, indicating the culmination of Holocene Atlantic influence. Christian Hjort and Lena Adrielsson, Department of Quaternary Geology, Lund Uniuersiry. Solvegaran 13, S-223 62 Lund, Sweden; Jan Mangerud and Stein Bondeuik, Department of Geology. Sectioii B , Unioersiry of Bergen, Allkgaten 41, N-SO14 Bergen, Norway; Jon Y . Landuik. U N I S , N-9170 Longyearbyen. Norway; Otto Saloigsen, Norsk Polarinsriturt. P. 0. Box 5072 Majorsma. N-0301 Oslo, Norway. Introduction T h e common mussel Mytilus edulis L. is mainly a n intertidal to shallow sub-tidal bivalve, which spreads with pelagic larvae and byssus drifting. I t does not live on Svalbard today, but living specimens attached to seaweed, boxes and other items, presumed to have drifted from the south, have been encountered several times during the last hundred years (Knipowitsch 1903a; Heintz 1926; Peacock 1983; Mangerud & Bolstad unpubl.). However. during the warmer parts of the Holo- cene, Mytilus was common on Svalbard, especially on the western coast (summary in Sal- vigsen et al. 1992: see Fig. 1). Reports from the colder northern and eastern parts of the archi- pelago are fewer. In the east, scattered finds had been made earlier on Edgeoya (Knipowitsch 1903b) and o n Svenskoya in the Kong Karls Land archipelago (Nathorst 1901; Hagg 1950). Nansen (1902) even found it as far east as Franz Josef Land. The PONAM expedition During the P O N A M (Polar North Atlantic Margins, Late Cenozoic Evolution. see Acknowl- edgements) expedition to eastern Svalbard in 1991, most major sections in Quaternary sedi- ments on E d g e ~ y a and Barentssya were studied, with extensive work being done also on western K o n g s ~ y a in Kong Karls Land. Mytilus was found in raised marine sediments at several localities, but only o n E d g e ~ y a (Hjort et al. 1992). where it occurs from ca 45 m a.s.1. to a few metres above the present shore. In some places it was very common, for example at Habenichtbukta on southwestern Edgeoya, close to Krausshavn where it was found during the Russian expedition in 1899 (Knipowitsch 1903b). T h e dated M-ytilus samples from Edgesya and t h e earlier Svenskoya find are listed in Table I . Most of the localities and finds were described by Hjort e t al. (1992) and also listed by Gulliksen et al. (1992), but four new dated samples, also collected during the P O N A M expedition, have now been added. All known occurrences on Edge- oya a r e indicated o n Fig. 2. Radiocarbon dates Eleven radiocarbon dates were made on Mytilus shells collected o n Edgesya during the FONAM expedition 1991 (Table 1). Eight of these were conventional datings made in Trondheim and Lund and three were AMS-datings made in Aarhus or Uppsala. T h e fragments found on 240 c'. Hjort et mi. Fig. 1. Svalbard. w t h dated Myrilus edtrlis finds according to Salvigsen et al (1992. open circles) and as added through this study (filled circles, details in Fig. 2 ) . Tnhlr I Radiocarbon dated M\.rllu.r rdrrlis samples from eastern S ~ a l h a r d . Except for no. 4 . which is froin Kong Karls Land and wd5 collected in 1898 (Nathorst 1901: Hagg 1950). all samples are from Edgeclya (Fig. 2 ) and were collected during the P O N A M expedition in I991 (Hjort et al. 1992: Gulliksen el al. 1992). The age5 are corrected for a rrservoir effect of -440 years (Mangerud 8: Gulliksen 1975). h"C is expressed as C r r on the P D B scale. t.ocalit! \mellcdalcn Hlafiorddaleii I < d d e d a l c n S\ensho!a Scidbreen Smelledalen Smelledalen Smelledalen hnelledalen Smelledalen Smelledalen f fabenichtbukta .~~~ Sample no. m J 5.1 Sh-707D R X - l i h 86-307 88-739 88-735 86-703A 87-6.53 86-702A Hl-655 87-654C 86-701 A 88-71 1 40 39 36 25 i n t i l l 35 37 31 15 28 27 1 Age 8 P 8755 2 175 ti510 t 1/11 8210 2 150 7260 i 100 7 ? 0 5 ? 115 7175 * l l t l 7095 -t 5 5 7oY5 2 135 7050 ? 1-11) h88.i z 85 5835 2 125 4960 2 80 ''C lab no T-YgIY T-Y9W AAR-837 AAR-853 T-9922 Tua-173 T-I0111 T-992 I T-10145 T-9920 Lu-3373 ud-3279 hl 'C Collector -0.2 0 1 - ( I 3 0.5 1 .o 0.3 0.3 -0.3 0.5 -0.6 - - J . Mangerud & S . Bondevik .I. Y . Landvik 0. Stubdrup & S . Bondevik G . A n d e r s o n C. Hjort .I. Mangerud 8: S . Bondcvik J . Mangerud J . Mangerud & S . Bondevik J . Mangerud J . Mangcrud J . Mangerud & S . Bondevik C. Hjort & L. Adrielsson Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard 241 78" 1 -77"30' I Svenskoya in 1898 were AMS-dated in Aarhus. All samples have been corrected for a reservoir effect of -440 years, according to Mangerud & Gulliksen (1975). 125 yrs BP and belong to those collected at the highest alti- tudes. The youngest dated shells, from 4960 ? 80 BP at Habenichtbukta, were those encountered at the lowest altitude, 4 m a.s.1. Our datings thus show that Mytilus immigrated to eastern Svalbard not later than ca 8800 BP and was still living there around 5000 BP. The oldest shells date from 8755 Discussion Present distriblction Although M y t i l u is not found living on Svalbard today, it penetrates far into southeastern Barents 212 C Hjort et nl. Sea (Peacock 1989) and u p along the western coast of Greenland (Funder B Weidick 1991). It even maintains populations o n the southeastern coast o f Greenland. uithin waters affected by the cold East Greenland Current (Hjort & Funder 1974: Funder RC Weidick 1991). I t also occurs at scattered localities along the eastern coast of Baffin Island. where Arctic Water flows south- ward in the Baffin-Labrador Current (Andrews 1972). Mytiliis may thus live under conditions where w m m e r sea-surface temperatures (SST's) approach 0°C. The presence of marginal popu- lations which live today in fjord areas inside cold- water currents (e.g. in the Ammassalik district i n southeastern Greenland), indicates an ability to colonise rather local areas with higher than aver- age SST's. This m a y occur during years with stronger than average Atlantic Water penetration (cf. cliccussion in Peacock 1989. p. 189). Hyp.sitlitwiicil distrihiirioti M y t i l [ i s had a much larger northward distribution during earlier parts of the Holocene and has become the classical exponent for warmer-than- present conditions in the Arctic. Svalbard was the area where this first became evident ( e . g . Blomhtrand 1861: Nathorst 1884; IHiigbom 1913: Feylinp-Hanssen l Y S 5 ) . According to the review by Salvigsen et al. (1991). i t immigrated t o the western coast of Svalbard before 9500 B P and lived there until around 3500 BP. Thereafter it briefly reim- migrated during the warm period around 1000 BP. Thus it seem\ to have appeared on eactern Svalbard some 500--900 vears later than on the western coast. The western and northern coasts are today the a r e a most affected by Atlantic Water. and that this general pattern prevailed also earlier during the Holocene is. for example. indicated by the mid-Holocene occurrence only on the central western coast of the boreal molluscs Zirpiiea crispata. Modiolus tiiodioliis, Arcrica islandica and Lirtoririn litroren ( Feyling-Hanssen 1955: Salvigsen et al. 1992: Mangerud & Svendsen 19Y2). According to our radiocarbon dates. the immigriition of "llyiihs to eastern Svalbard roughl! coincided with the first appearance of boreal molluscs on the west coast. which took place around 8700 B P (Salvigsen et al. 1993). Thus i t seem3 that it managed to colonise these eastern parts a 5 an effect of a maximum Atlantic Water influx to the region. But M y t i l i s lived o n along the shores of Edgeaya well after the boreal period on the western coast had come t o an e n d , as it did around 7700 BP. Nor was our youngest M y i i l u s date. from ca 5000 BP, from a population on the verge of extinction. It then still lived in profusion in a local shallow lagoon environment in Hab- enichtbukta (Adrielsson e t al. 1992). Today the waters around Edgeaya and Kong Karls Land are dominated by the southwesterly How of Arctic Water in the East Spitsbergen Current (e.g. Loeng 1991). It seems that a pre- condition for the immigration of Mytilus into this area. and for its persistence there during ca 4000 years. must have been a weakening of this cold current and a much stronger influx of Atlantic Water than today. T h e foraminifera1 record in marine sediment cores from western Franz Josef Land, northeast of our study area and much further away from the Atlantic source supports this. It indicates that the most favourable marine conditions there. with the strongest Atlantic influence, were between 7000-5000 B P (Polyak & Solheim 1994). How quickly the balance between warmer Atlantic and colder Arctic waters may indeed shift. over a few decades or less. has recently been documented from the northern coast of Svalbard by Eggertsson (1994). with the help of driftwood studies. T h e same pattern of early to mid-Holocene weakening of cold water outflows from the Polar Basin. with a markedly stronger Atlantic influ- ence. has been suggested for both the East Green- land Current and the Baffin-Labrador Current, using Myiilus dates (Andrews 1972; Hjort RC Fun- der 1974; Funder & Weidick 1991). A study by Koc & Jansen (1991), based o n oxygen isotope and diatom stratigraphy in d e e p sea cores from the Greenland Sea, confirms that this enhanced Atlantic influence began to affect the coast of central East Greenland ca 8500 B P , which is roughly when M y t h s immigrated (Hjort & Fun- der 1974). T h e Atlantic influence diminished from ca 5000 BP. coinciding with the disappearance of Myrilus. This further illustrates the close relation- ship between oceanographic climatic conditions and the geographic distribution of this pelagically spreading indicator bivalve! 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